Process of forming electric-incandescent-lamp filaments.



V To all whom it may concern.

, dilute hydrochloric acid. There then remains on the *r %TATE% Paranarrron.

WERNER VON BOLTON, OF CHARLOTTENBURG, AND FELIX HARTMANN, OF BERLIN,GER- MANY, ASSIGNORS TO SIEMENS & OF GERMANY.

PROCESS OF FOR MNG ELECTRIC-TNCANEESGENT-L ...i

HALSKE A. G., OF BERLIN, GERMANY, A CORPORATION k Specification ofLetters Patent.

PatentedAug. 1'0, 1909.

Application med. February 3,1909. sextant. e'ie,1c7.

Be it known that We, WERNER VON BoL- TON and FELIX HARTMANN, subjects ofthe Czar of Russia and the German Emperor, respectively, andres'iding atOharlottenburg an Berlin, Germany, res ectively, have invented certainnew an useful Improvements in'Processes of FormingElectric-Incandescent-Lamp Filaments, of which the following is aspecification.

Our invention relates to electric incandescent lamps and is morearticularly concerned wlth the filaments f dr such lamps.

It has already been proposed in the United States patent applicationSerial N 0. 337,122 filed October 2, 1906 to press tungsten powder intoa tube composed of ductile metal and to then draw out or roll thisductile tube together'with the metallic powder which it contains intofilamentary form.

Now in accordance with the present invention, before the tungsten powderis placed into the tube we place into the latter another tube which alsoconsists of a very ductile metal, as, for example, copper, silver ornickel. The powdered tungsten is then inserted uniformly into this innertube, the ends of the tube are sealed, for example by screwing orwedging copper plugs into them, and the tube is thereupon rolled ordrawn out, or first rolled and then rolled out still further.

A steel tube is preferabl employed as the outer tube. After the d iawingo eration the outer tube is removed, for examp e, when a steel tube isemployed, by dissolving it in or sulfuric acid. drawn wire a thincoating or shell consisting of the material of the inner. tube. Thisconsiderably facilitates the manipulation of the core of tun sten, sothat it can be brought more readi y into the desired shapes and theremaining manipulations necessary for completing the manufacture of thelamp can be carrie out more easil Lastly, the thin coating of thetungsten ament. can then be removed by heating it highly in a vacuum orin a rarefied atmosphere, for exam le in a rarefied atmosphere ofhydrogen. Torthis purpose,after the body has been placed into a suitablereceiver and the gas contained in the latter has been rarefied, anelectric current is sent through the filament. When the temperature hasrisen suificientl the metal forming the casing or shell begins tovaporize at one place. In a short time it will be found that thevaporizing process has extended along the entire length of the filamentand the finished incandescent filament is obtained.

A drawn steel tubemm. long, of 8 mm. exterior, and 4 mm. interior,diameter can be em loyed for example, a copper, silver or nic el tube ofhaving a wall 0.2 mm. thick being fitted exact y into it. Fine, sifted,powdered tungsten is now shaken loosely into the inner tube. I It ispreferable not'to press this powder too firmly, but'onl to settle ituniformly inthe tube which can be done by lightly, taping the tube on ahard surface. Particuarly uniform results are then obtained, and

simultaneously a certain degree ofporosityis obtained Which hasadvantages in many respects. The tube is now closed with plugs of copperor silver about 5 mm. long and is then rolled or drawn.

drawn out to the very finest Wires and after the outer shell has beenremoved a very,

usable incandescent filament is obtained.

During the vaporization of the shell of cop er, silver, and the like,Which is directly on t e tungsten filament an alloy of tungsten with theincasing metal can be formed under certain circumstances. Such an alloycan readily be obtained articularly when the temperature of the fi amentis driven very rapidly too close to the point at which the incasingmetal va orizes. These allo shave a more or less high degree of ductii-ty, so t at .it is possible'to. subject the filaments alloyed in thismanner to an additional rolling or drawing process.

be driven ofi later. The formation of such alloys is particularlyfacilitated b thetungsten bein-pressed1i0t too firm yinto the tube inwhich it is to be drawn. In exactly the same manner asis here describedwith reference to tungsten, other highly refractory metals, erwise, canalso process. 4

What we claim as our inventionand desire besubjected to a drawing tosecure by Letters Patent is:

1. The hereindescribed process for produc- I V By heating the fila menthighly the additional metal can then 4 mm. exterior diameter and Such atube'can be 100 which are difficult to draw othl working the "powderinto filamentary form.

ing a tube of ductile .metal a tube of another ductile metal, insertingrefractory metal powder into the inner tube, and. subsequently tubesBand the refractory metal 2, The hereindescribed process for iroducinfilaments which consists in fittin into a 'tu e of ductile metal a tubeof a dlfl'erent,

very ductile metal, inserting tungsten powder into the latter tube,subsequently working the tubes and the tungsten powder into filamentswhich consists in inserting into filamentary form, removing the outertube, 1

names to this specification in the presence of two witnesses.

WERNER VON BOLTON. I FELIX HARTMANN.

Witnesses:

HENRY HASPER, WoLDEMAR HAUPT,

